TY - JOUR A1 - Hermanns, Jolanda T1 - Scaffolding for chemistry students – which tools are assessed as being more helpful BT - Stepped supporting tools or task navigators? JF - Chemistry Teacher International N2 - In this paper the use of two different scaffolds in a seminar on the topic of heterocycles is discussed. The students first used both scaffolds (stepped supporting tools and a task navigator) on two tasks and could then choose for one other task the scaffold that suited them more. The scaffolds were evaluated in a mixedmethods study by the use of questionnaires and the conducting of a focus group interview. Both scaffolds were assessed as being helpful. However, students who thought they didn’t need different sorts of tips, as provided by the task navigator, chose the stepped supporting tools. All students reflected on their use of the scaffolds; their choices for one of both are therefore well-founded. As the reasons for choosing the scaffold are very individual, in future seminars both types of scaffolds will be provided. KW - organic chemistry KW - scaffolding KW - self-regulated learning KW - solving of tasks Y1 - 2020 U6 - https://doi.org/10.1515/cti-2020-0019 SN - 2569-3263 PB - De Gruyter CY - Berlin ER - TY - GEN A1 - Hermanns, Jolanda T1 - Scaffolding for chemistry students – which tools are assessed as being more helpful BT - Stepped supporting tools or task navigators? T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - In this paper the use of two different scaffolds in a seminar on the topic of heterocycles is discussed. The students first used both scaffolds (stepped supporting tools and a task navigator) on two tasks and could then choose for one other task the scaffold that suited them more. The scaffolds were evaluated in a mixedmethods study by the use of questionnaires and the conducting of a focus group interview. Both scaffolds were assessed as being helpful. However, students who thought they didn’t need different sorts of tips, as provided by the task navigator, chose the stepped supporting tools. All students reflected on their use of the scaffolds; their choices for one of both are therefore well-founded. As the reasons for choosing the scaffold are very individual, in future seminars both types of scaffolds will be provided. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1108 KW - organic chemistry KW - scaffolding KW - self-regulated learning KW - solving of tasks Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-491001 SN - 1866-8372 IS - 1108 ER - TY - THES A1 - Markushyna, Yevheniia T1 - Modern photoredox transformations applied to the needs of organic synthesis N2 - Abstract. Catalysis is one of the most effective tools for the highly efficient assembly of complex molecular structures. Nevertheless, it is mainly represented by transition metal-based catalysts and typically is an energy consuming process. Therefore, photocatalysis utilizing solar energy is one of the appealing approaches to overcome these problems. A great alternative to classic transition metal-based photocatalysts, carbon nitrides, a group of organic polymeric semiconductors, have already shown their efficiency in water splitting, CO2 reduction, and organic pollutants degradation. However, these materials have also a great potential for the use in functionalization of complex organic molecules for synthetic needs as it was shown in recent years. This work addresses the challenge to develop efficient system for heterogeneous organic photocatalysis, employing cheap and environmentally benign photocatalysts – carbon nitrides. Herein, fundamental properties of semiconductors are studied from the organic chemistry standpoint; the inherent properties of carbon nitrides, such as ability to accumulate electrons, are deeply investigated and their effect on the reaction outcome is established. Thus, understanding of the electron charging processes allowed for the synthesis of otherwise hardly-achieved diazetidines-1,3 by tetramerization of benzylamines. Furthermore, the high electron capacity of Potassium Poly(heptazine imide)s (K-PHI) made possible a multi-electron reduction of aromatic nitro compounds to bare or formylated anilines. Additionally, two deep eutectic solvents (DES) were designed as a sustainable reaction media and reducing reagent for this reaction. Eventually, the high oxidation ability of carbon nitride K-PHI is employed in a challenging reaction of halide anion oxidation (Cl―, Br―) to accomplish electrophilic substitution in aromatic ring. The possibility to utilize NaCl solution (seawater mimetic) for the chlorination of electron rich arenes was shown. Eventually, light itself is used as a tool in a chromoselective photocatalytic oxidation of aromatic thiols and thioacetatas to three different compounds, using UV, blue, and red LEDs. All in all, the work enhances understanding the mechanism of heterogeneous photocatalysis in synthetic organic reactions and therefore, is a step forward to the sustainable methods of synthesis in organic chemistry. N2 - Abstrakt. Die Katalyse ist eines der effektivsten Werkzeuge für den hocheffizienten Aufbau komplexer molekularer Strukturen. Dennoch wird sie hauptsächlich durch Katalysatoren auf der Basis von Übergangsmetallen repräsentiert und ist typischerweise ein energieaufwendiger Prozess. Daher ist die Photokatalyse unter Nutzung der Sonnenenergie einer der attraktiven Ansätze zur Überwindung dieser Probleme. Kohlenstoffnitride, eine Gruppe organischer polymerer Halbleiter, haben ihre Effizienz bei der Wasserspaltung, der CO2-Reduktion und dem Abbau organischer Schadstoffe bereits unter Beweis gestellt. Diese Materialien haben jedoch auch ein großes Potenzial für die Funktionalisierung komplexer organischer Moleküle für synthetische Zwecke, wie sich in den letzten Jahren gezeigt hat. Diese Arbeit befasst sich mit der Herausforderung, ein effizientes System für die heterogene organische Photokatalyse zu entwickeln, bei dem billige und umweltfreundliche Photokatalysatoren – Kohlenstoffnitride – zum Einsatz kommen. Dabei werden grundlegende Eigenschaften von Halbleitern aus organisch-chemischer Sicht untersucht; die inhärenten Eigenschaften von Kohlenstoffnitriden, wie die Fähigkeit zur Elektronenanreicherung, werden eingehend untersucht und ihr Einfluss auf das Reaktionsergebnis festgestellt. So ermöglichte das Verständnis der Elektronenladungsvorgänge die Synthese von sonst kaum erreichten Diazetidinen-1,3 durch Tetramerisierung von Benzylaminen. Darüber hinaus ermöglichte die hohe Elektronenkapazität von Kalium-Polyheptazinimid (K-PHI) eine Mehrelektronenreduktion von aromatischen Nitroverbindungen zu „nackten“ oder formylierten Anilinen. Zudem wird die hohe Oxidationsfähigkeit von Kohlenstoffnitrid, K-PHI, in einer herausfordernden Reaktion der Oxidation von Halogenidanionen genutzt, um eine elektrophile Substitution im aromatischen Ring zu erreichen. Schließlich wird das Licht selbst als Werkzeug in einer chromoselektiven photokatalytischen Oxidation von aromatischen Thiolen und Thioacetaten verwendet, um drei verschiedene Verbindungen unter Verwendung von UV-, blauen und roten LEDs zu syntetisieren. Alles in allem verbessert die Arbeit das Verständnis des Mechanismus der heterogenen Photokatalyse in synthetischen organischen Reaktionen und ist daher ein Schritt vorwärts zu nachhaltigen Synthesemethoden in der organischen Chemie. KW - photocatalysis KW - carbon nitride KW - organic chemistry KW - photoredox catalysis KW - Photochemie KW - Photokatalyse Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-477661 ER -